The present invention relates to a knife assembly for a chipping canter or similar small log sawmill device which may be readily and simply removed for maintenance or replacement. The knife assembly is especially well adapted for use on chipping canters having a plurality of knife retaining rotatable segments mounted on a common shaft so as to define a generally cylindrical chipper head when in operation. At the present time approximately half of the saw logs in the United States and Canada are processed through primary breakdown devices including a chipper as an integral part. These chippers create flat surfaces on one or more sides of the log to simplify downstream processing. The portions of the log that would formerly have been removed as slabs are thereby converted into saleable pulp chips. Such devices are frequently called canters since the log is usually configured by the chippers so that it is converted into one or more cants of predetermined dimensions after subsequent primary sawing. A cant is a sawn or otherwise processed piece of wood of generally rectangular cross section intended for further processing into boards or dimension lumber.
The most popular chipping canters are configured to have a plurality of individual segments stacked one adjacent another on a common shaft. Each segment normally has two replaceable peripheral cutter knives. Adjacent heads on a given shaft are normally rotated so that the cutter knives are displaced by 90.degree.. Knives are retained in notches on the periphery of the segment by a heavy dog fastened with a single bolt.
One device using chippers of this type is sold as the Chip-N-Saw.RTM. chipping canter/primary log breakdown unit. Chip-N-Saw is a registered trademark of Kockums CanCar, a Hawker Siddeley company of Vancouver, B.C.
The knives of the chipping canter of the type described above have a cutting edge approximately 50 mm in length and are made of a single piece of steel. The top-to-bottom dimension of these knives changes as they are ground for sharpening. In order to compensate for this, before replacement on the machine, they are placed in a jig and a shim of babbit metal is poured adjacent the bottom surface. In this manner a constant cutting radius can be maintained. In some positions on a typical installation the knives are routinely replaced as frequently as every four hours. Depending on the maximum log size to be processed through the machinery, from 20 to 50 chipper segments employing twice this many knives are used. Knife replacement and maintenance forms a major item of operating expense. After grinding for resharpening, the babbitt shim must be stripped from the base. A number of knives are placed side by side in a gib and shimmed or otherwise adjusted to bring the edges to a common height. Then a contoured grinding wheel traverses the knives to resharpen them. Each individual knife must them be removed and rebabbitted before it can again be installed on the machine. The grinding wheels themselves represent a significant expense. Their life is relatively short since they must frequently be dressed to maintain a precise and complex edge configuration.
Others have in the past looked at chipping canters with an object of simplifying knife maintenance. One such effort is described in U.S. Pat. No. 3,356,114 to Noel. Here the knife is a simple arcuate or crescentic-shaped blade which extends the full length of an elongated cylindrical chipper head. This blade is frictionally held in place in an arcuate seat on the chipper head by a dog and jib arrangement. Normally the base will be babbitted or otherwise shimmed to ensure a constant cutting radius. Another example of a chipping knife assembly that was designed with maintainability in mind is that disclosed in U.S. Pat. No. 4,667,713 to Wright. In this patent a multi-piece knife assembly includes a separate slidable knife assembly mounted on a removable knife holder. The slidable and removable knife member can be sharpened and then adjusted when it is replaced in its knife holder for precision chipping. This particular design is relatively complex and is expensive to manufacture. When this chipping knife assembly is in use it is one that has many interconnected parts and therefore is susceptible to breakage plus being difficult to maintain proper alignment during continued operations. This particular type of chipping knife assembly resembles somewhat those complex saw teeth structures used in saws. The following U.S. patents are representative of some of the earlier variations in this generic concept: Woodcook, U.S. Pat. No. 1,356,682; Brown, U.S. Pat. No. 1,140,021; Freas, U.S. Pat. No. 1,831,705; and Charlton, U.S. Pat. No. 2,117,147. These and many subsequent similar patents are primarily directed to minor variations in tooth configuration to ensure tightness and stability during operation.
There has been a long-felt need within the sawmilling industry for a chipping canter knife assembly which has readily replaceable individual knife members appropriately incorporated into the overall assembly and which is relatively simple, economical and readily maintained. These needs have now been fulfilled by the knife assembly of the present invention.